The first botnet (networks of computers responsible for sending out massive amounts of spam) was created by Khan C. Smith. Earthlink, the 3rd largest ISP at the time, exposed him in August, 2001 when they filed a lawsuit against him. It turned out that Khan was responsible for a whopping 25% of the spam that was being sent in those days, and Earthlink won $25 million from the lawsuit. The 2003 CAN-SPAM Act was signed into law soon afterwards.